...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CENTRAL PLAINS...

...SYNOPSIS... ALTHOUGH MODELS DIFFER SOMEWHAT WITH THE AMPLIFICATION OF A TROUGH OVER THE ERN STATES...GENERAL AGREEMENT EXISTS WITH THE TIMING OF A COUPLE OF EMBEDDED SHORTWAVE TROUGHS EXPECTED TO TRACK EWD ACROSS THE MID ATLANTIC STATES THIS FORECAST PERIOD. MEANWHILE...HEIGHTS ARE EXPECTED TO RISE UPSTREAM FROM THE LOWER MO TO UPPER MS VALLEYS AS FURTHER AMPLIFICATION OCCURS WITH THE WRN TROUGH.

IN THE LOW LEVELS...A SURFACE LOW AND TRAILING COLD FRONT WILL SPREAD EWD FROM THE OH/TN VALLEY...REACHING IN LEE OF THE CENTRAL AND SRN APPALACHIANS BY 12Z FRIDAY. FARTHER W...A LEE CYCLONE WILL DEEPEN ACROSS SERN CO BENEATH SWLY FLOW ALOFT AND THEN MOVE INTO WRN KS THURSDAY NIGHT.

...PARTS OF THE CENTRAL PLAINS... SLY LOW LEVEL FLOW EAST OF THE CO CYCLONE WILL SPREAD MOISTURE NWD ACROSS THE PLAINS AND ALSO INTO THE MID MS VALLEY...WITH WNWWD MOISTURE ADVECTION INTO WRN NEB/NERN CO. PLUME OF STEEP MIDLEVEL LAPSE RATES/EML EXTENDING ACROSS THE MOISTURE RETURN WILL SUPPORT A CORRIDOR OF STRONG INSTABILITY EXTENDING FROM CENTRAL/ERN OK/KS TO THE CENTRAL DAKOTAS THURSDAY AFTERNOON...WITH WEAKER INSTABILITY INTO THE NERN CO/WRN NEB.

UPSLOPE FLOW ALONG THE NRN PERIPHERY OF THE CO SURFACE LOW AND FORCING FOR ASCENT ATTENDANT TO A MIDLEVEL IMPULSE INDICATED BY THE 14/00Z ECMWF SUGGESTS AFTERNOON TSTM DEVELOPMENT WILL BE POSSIBLE OVER NERN CO/SERN WY INTO WRN NEB. DESPITE WEAKER INSTABILITY... VERY STEEP MIDLEVEL LAPSE RATES AND EFFECTIVE BULK SHEAR OF 40-55 KT WILL PROVE FAVORABLE FOR HIGH BASED SUPERCELLS. UPSCALE GROWTH OF THE HIGH PLAINS ACTIVITY IS POSSIBLE AS LOW LEVEL WAA INCREASES ACROSS THE CENTRAL PLAINS...WITHIN THE NOSE OF A STRENGTHENING CENTRAL/SRN PLAINS SLY LLJ. THUS...THE SLIGHT RISK EXTENDS EWD TO ACCOUNT FOR MAINLY ELEVATED STORMS PRODUCING HAIL AND SOME STRONGER WIND GUSTS AS THE MIDLEVEL IMPULSE PROGRESSES TOWARD ERN NEB TO SRN MN LATE IN THE PERIOD.

...THERE IS A SLGT RISK OF SVR TSTMS FROM CENTRAL/SERN VA TO ERN/SERN GA...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CENTRAL PLAINS...

...SYNOPSIS... MODELS ARE IN BETTER AGREEMENT WITH THE TRACK AND EVOLUTION OF THE CURRENT NRN PLAINS SHORTWAVE TROUGH FOR THE DAY 2 PERIOD... WITH THIS SYSTEM MOVING FROM THE WRN GREAT LAKES TO THE UPPER OH VALLEY/CENTRAL APPALACHIANS BY 12Z FRIDAY. MEANWHILE...A COUPLE OF MIDLEVEL SHORTWAVE TROUGHS WILL EJECT NEWD FROM THE BASE OF A LONGWAVE TROUGH CONTINUING TO DEVELOP ACROSS THE FULL EXTENT OF THE WRN STATES. THESE IMPULSES SHOULD REACH THE CENTRAL/NRN HIGH PLAINS BY LATE THURSDAY AFTERNOON AND THEN PROCEED ACROSS THE DAKOTAS AND CENTRAL PLAINS THURSDAY NIGHT. BETWEEN THE E AND W TROUGHS...A RIDGE WILL BUILD NWD FROM THE LOWER MO VALLEY TO UPPER MS VALLEY/WRN GREAT LAKES.

IN THE LOW LEVELS...A SURFACE LOW AND TRAILING COLD FRONT WILL SPREAD EWD FROM THE OH/TN VALLEYS...WITH THE FRONT MOVING EAST OF THE CENTRAL/SRN APPALACHIANS BY 17/00Z. FARTHER W...A LEE CYCLONE WILL DEEPEN ACROSS ERN CO BENEATH SWLY FLOW ALOFT AND THEN MOVE INTO WRN/CENTRAL KS THURSDAY NIGHT. MEANWHILE...A SURFACE FRONT EXPECTED TO STALL FROM THE MID SOUTH WWD TO NORTH TX DURING DAY 1 WILL LIFT NWD THURSDAY AS A WARM FRONT. THIS BOUNDARY SHOULD REACH NRN KS TO SRN MO BY LATE THURSDAY AFTERNOON.

...MID-ATLANTIC AND SERN STATES... A WEAKENING LEAD IMPULSE SHOULD BE MOVING ACROSS THE MID-ATLANTIC STATES/DELMARVA REGION DURING THE EARLY PART OF DAY 2...WITH NEUTRAL TO WEAK HEIGHT RISES IN ITS WAKE THROUGH THURSDAY AFTERNOON. SHOWERS AND EMBEDDED TSTMS ARE FORECAST TO TRACK ACROSS MD/VA/DEL AND NC THURSDAY MORNING/EARLY AFTERNOON...AND SHOULD TEND TO LIMIT STRONGER DESTABILIZATION ACROSS THESE AREAS. MEANWHILE... SSWLY LOW LEVEL WINDS WILL SPREAD MOISTURE NWD IN LEE OF THE SRN/CENTRAL APPALACHIANS. THIS COMBINED WITH SURFACE HEATING IN THE WAKE OF MORNING ACTIVITY AND AHEAD OF THE APPROACHING COLD FRONT SHOULD SUPPORT A NARROW CORRIDOR OF MODERATE INSTABILITY FROM CENTRAL VA INTO WRN NC...AND SWD ACROSS THE SERN STATES.

EFFECTIVE BULK SHEAR SHOULD BE STRONGER /UP TO 35 KT/ ACROSS VA/NC SUPPORTIVE FOR POTENTIAL SUPERCELLS...WHILE FARTHER S...BULK SHEAR SHOULD BE MORE FAVORABLE FOR MULTICELLS ACROSS SC/GA. GIVEN THESE FACTORS COMBINED WITH SOME UNCERTAINTY IN DEGREE OF DESTABILIZATION WITH NWD EXTENT DUE TO EARLY DAY CONVECTIVE CLOUDINESS...15 PERCENT SEVERE PROBABILITIES WILL BE MAINTAINED WITH THIS OUTLOOK ISSUANCE.

...PLAINS STATES TO THE LOWER MO VALLEY... SLY LOW LEVEL FLOW WILL RETURN MOISTURE NWD THROUGH THE CENTRAL PLAINS TO THE MID MO VALLEY AND NEWD INTO THE LOWER MO/MID MS VALLEYS. THIS MOISTURE COMBINED WITH DIABATIC HEATING BENEATH A PLUME OF VERY STEEP MIDLEVEL LAPSE RATES EXTENDING NEWD ACROSS THE PLAINS STATES TO LOWER MO VALLEY WILL RESULT IN STRONGLY UNSTABLE AIR MASS. MLCAPE 2000-3000 J/KG IS EXPECTED TO EXTEND FROM NRN AR NWWD INTO NRN KS TO SRN SD.

UPSLOPE FLOW ALONG THE NRN PERIPHERY OF THE CO SURFACE LOW AND FORCING FOR ASCENT ATTENDANT TO A MIDLEVEL IMPULSE SUGGEST AFTERNOON TSTM DEVELOPMENT WILL BE POSSIBLE OVER NERN CO INTO CENTRAL/ERN WY AND THE NEB PANHANDLE. DESPITE WEAKER INSTABILITY WITH WWD EXTENT...VERY STEEP MIDLEVEL LAPSE RATES AND EFFECTIVE BULK SHEAR OF 40-55 KT WILL PROVE FAVORABLE FOR HIGH BASED SUPERCELLS. UPSCALE GROWTH OF THE HIGH PLAINS ACTIVITY IS POSSIBLE AS LOW LEVEL WAA INCREASES ACROSS THE CENTRAL PLAINS...WITHIN THE NOSE OF A RATHER BROAD STRENGTHENING CENTRAL/SRN PLAINS SLY LLJ. THUS...THE SLIGHT RISK ALSO EXTENDS EWD TO ACCOUNT FOR OVERNIGHT ELEVATED STORMS PRODUCING HAIL AND SOME STRONGER WIND GUSTS AS THE MIDLEVEL IMPULSE PROGRESSES TOWARD ERN NEB TO SRN MN LATE IN THE PERIOD. A FEW MODELS SUGGEST A SEPARATE TSTM INITIATION AREA ACROSS NRN KS/ERN NEB WITH THIS ACTIVITY SPREADING INTO IA/SRN MN THURSDAY NIGHT. DEGREE OF INSTABILITY AND DEEP LAYER SHEAR WILL SUPPORT A SEVERE THREAT WITH THIS ACTIVITY.

...PARTS OF THE OH VALLEY... FORCING FOR ASCENT ATTENDANT TO THE SHORTWAVE TROUGH AND EXIT REGION OF ACCOMPANYING 50 KT WNWLY MIDLEVEL JET TRACKING ESEWD ACROSS THIS REGION ON THURSDAY SHOULD SUPPORT TSTM DEVELOPMENT WITHIN A MARGINALLY UNSTABLE ENVIRONMENT. WEAK MIDLEVEL LAPSE RATES AND SOME RESIDUAL MOISTURE FROM DAY 1 COMBINED WITH DIABATIC HEATING SHOULD RESULT IN MLCAPE OF 500-1000 J/KG. EFFECTIVE BULK SHEAR OF 30-35 KT SUGGESTS A FEW ORGANIZED STORMS WILL BE POSSIBLE...THOUGH WEAK INSTABILITY SHOULD LIMIT OVERALL SEVERE WEATHER THREAT.

BY FRIDAY NIGHT HOWEVER...DEEP CLOSED LOW OVER SRN SASKATCHEWAN WILLESTABLISH A BROAD SWLY LOW-MID LEVEL FLOW ACROSS THE PLAINS AND INTOTHE MID/UPPER MS VALLEY. AS THIS TAKES PLACE...A LINGERING FRONTALBOUNDARY FROM THE CENTRAL PLAINS...EWD THROUGH THE UPPER OH VALLEYWILL BEGIN TO MOVE NWD AS A WARM FRONT. THIS INCREASING SURGE OFTROPICAL AIR WILL AID IN THE DEVELOPMENT OF YET ADDITIONAL ROUNDS OFELEVATED THUNDERSTORMS AND CONVECTIVE COMPLEXES. THERE CONTINUES TOBE SOME MODEL DIFFERENCES REGARDING THE TIMING OF WARM FRONTALPASSAGE OVER THE WEEKEND. THE GFS IS THE MOST AGGRESSIVE ONBRINGING THIS FRONT THROUGH NRN IL/NWRN INDIANA...WHILE THE NAM/EUROSOLUTIONS KEEP ELY SURFACE-BOUNDARY LAYER FLOW GOING THROUGH ATLEAST SUNDAY. REGARDLESS OF THIS FRONTAL POSITION...WILL CONTINUEA MENTION OF THUNDERSTORMS FROM FRIDAY NIGHT THROUGH THE EXTENDEDPERIOD. IF GFS TURNS OUT TO BE CORRECT...WE WILL BREAK INTOTROPICAL AIR...BUT BE VERY UNSTABLE THROUGH THE PERIOD TO THEPOINT THAT A RANDOM SNEEZE MAY SET OFF THUNDERSTORMS. IF THE OTHERSOLUTIONS ARE MORE ACCURATE...THEN WE WILL REMAIN IN A ZONE OFSTRONGER LOW LEVEL MOISTURE CONVERGENCE AND AN ONGOING RISK OFMORE ORGANIZED THUNDERSTORM COMPLEXES. THE VARIATIONS IN MODELFORECAST FRONTAL POSITION PRESENT MORE INCONSISTENCY/UNCERTAINTYIN MAX TEMPERATURE FORECASTS AS OPPOSED TO THE PRECIPITATIONOUTLOOK.

...THERE IS A SLGT RISK OF SVR TSTMS TODAY AND TONIGHT ACROSS PARTS OF THE CENTRAL PLAINS INTO THE MID/LOWER MISSOURI VALLEY REGION...

...THERE IS A SLGT RISK OF SVR TSTMS TODAY ACROSS PARTS OF THE UPPER OHIO VALLEY AND MID ATLANTIC STATES...

...SYNOPSIS... MODELS INDICATE LITTLE CHANGE TO THE LARGE-SCALE FEATURES WITHIN THE PREVAILING SPLIT UPPER FLOW IMPACTING NORTH AMERICA THROUGH THIS FORECAST PERIOD. WITHIN ONE BRANCH OF STRONGER FLOW TRAVERSING THE NORTHERN AND CENTRAL TIER OF THE U.S...A BROAD CLOSED LOW APPEARS LIKELY TO LINGER NEAR THE NORTHERN ROCKIES. BUT A SIGNIFICANT SHORT WAVE IMPULSE IS PROGGED TO MIGRATE AROUND THE SOUTHERN PERIPHERY OF ITS CIRCULATION CENTER...DIGGING ACROSS THE NORTHERN INTERMOUNTAIN REGION DURING THE DAY...BEFORE TURNING EASTWARD INTO THE ROCKIES TONIGHT. DOWNSTREAM...ANOTHER MUCH MORE COMPACT CLOSED LOW IS EXPECTED PROGRESS ACROSS SOUTHERN PORTIONS OF THE GREAT LAKES REGION...TOWARD THE UPPER OHIO VALLEY...TO THE SOUTH OF A YET ANOTHER CLOSED LOW SHIFTING SOUTH SOUTHWESTWARD TOWARD SOUTHERN HUDSON/JAMES BAY. FARTHER SOUTH...HIGH-LEVEL TROUGHING PROBABLY WILL PERSIST OVER MUCH OF THE SOUTHEAST AND GULF OF MEXICO...BETWEEN SUBTROPICAL HIGH CENTERS OVER THE NORTHERN MEXICAN PLATEAU AND OVER THE LOWER LATITUDE ATLANTIC.

...CENTRAL PLAINS INTO MID/LWR MISSOURI VALLEY... GUIDANCE CONTINUES TO SUGGEST THAT AN IMPULSE EMERGING FROM THE WESTERN TROUGH MAY CONTRIBUTE TO INCREASING CONVECTIVE DEVELOPMENT BY THE 15-18Z TIME FRAME...BASED WITHIN A ZONE OF ENHANCED LOWER/MID TROPOSPHERIC WARM ADVECTION ACROSS NORTH CENTRAL AND NORTHEAST KANSAS. THIS IS EXPECTED TO OCCUR COINCIDENT WITH A RETURN FLOW OF MOISTURE NOW PRESENT ALONG AND SOUTH OF A WEAKENING FRONT ACROSS THE RED RIVER VALLEY/OZARKS PLATEAU REGION. IN THE PRESENCE OF MODERATELY STRONG SHEAR BENEATH 30-40 NORTHWESTERLY 500 MB FLOW...POTENTIAL APPEARS TO EXIST FOR AN ORGANIZING MESOSCALE CONVECTIVE SYSTEM BY MID DAY NEAR THE KANSAS CITY AREA...ON THE EDGE OF VERY WARM...AND MORE STRONGLY CAPPING...ELEVATED MIXED LAYER AIR ADVECTING ACROSS THE CENTRAL/SOUTHERN PLAINS. AS THE BOUNDARY LAYER ACROSS THE MISSOURI OZARKS DESTABILIZES WITH MOISTURE ADVECTION...DAYTIME HEATING AND STEEPENING MID-LEVEL LAPSE RATES...A SIGNIFICANT CONVECTIVELY GENERATED COLD POOL MAY DEVELOP WITH A RISK FOR STRONG DAMAGING WINDS. AS THIS ACTIVITY DEVELOPS SOUTHEASTWARD THROUGH PARTS OF CENTRAL/SOUTHERN MISSOURI...A TRAILING OUTFLOW BOUNDARY INTO PARTS OF SOUTHEAST AND CENTRAL KANSAS MAY REMAIN A FOCUS FOR NEW STORM DEVELOPMENT...PARTICULARLY TONIGHT...AS A STRONG SOUTHERLY LOW-LEVEL JET DEVELOPS ACROSS THE PLAINS.

ELSEWHERE...FORCING DOWNSTREAM OF THE MAIN UPPER IMPULSE OVER THE INTERMOUNTAIN WEST MAY CONTRIBUTE TO ADDITIONAL STRONG/SEVERE STORM DEVELOPMENT BY LATE THIS AFTERNOON...WITHIN A MOISTENING AND DESTABILIZING UPSLOPE BOUNDARY LAYER FLOW ACROSS THE NORTH CENTRAL HIGH PLAINS. VEERING WINDS WITH HEIGHT...FROM EASTERLY AT LOWER LEVELS TO MODESTLY STRONG SOUTHWESTERLY AT MID-LEVELS... SHOULD PROVIDE SUFFICIENT SHEAR FOR SUPERCELLS INITIALLY. UPSCALE GROWTH INTO A MESOSCALE CONVECTIVE SYSTEM THEN APPEARS LIKELY THIS EVENING...AS ACTIVITY DEVELOPS EASTWARD ACROSS WESTERN NEBRASKA...AIDED BY STRONG INFLOW OF AIR WITH CAPE OF 2000-3000+ J/KG. THIS PROBABLY WILL BE ACCOMPANIED BY A SIGNIFICANT COLD POOL WITH STRONG DAMAGING WIND GUSTS.

OTHER MORE ISOLATED STRONG/SEVERE STORM DEVELOPMENT MAY ALSO OCCUR LATE THIS AFTERNOON AND EVENING ALONG THE DRY LINE ACROSS PARTS OF WESTERN KANSAS INTO THE TEXAS/OKLAHOMA PANHANDLE REGION...WHERE A HOT AND DEEPLY MIXED BOUNDARY LAYER WILL BE SUPPORTIVE OF STRONG DOWNBURSTS...PERHAPS SOME HAIL.

...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN PARTS OF THE NRN/CENTRAL PLAINS SEWD THROUGH THE OH VALLEY...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PART OF THE MID-ATLANTIC STATES...

...SYNOPSIS... AN OMEGA BLOCK UPPER AIR PATTERN WILL PERSIST FROM THE NRN EXTENT OF THE U.S. AND CANADA...WITH ATTENDANT CLOSED LOWS CENTERED OVER WRN CANADA AND QUEBEC. GRADUAL HEIGHT RISES ARE EXPECTED FROM THE LOWER MS VALLEY NEWD INTO THE OH VALLEY TO MID-ATLANTIC STATES. A SHORTWAVE TROUGH...CURRENTLY TRACKING SSEWD THROUGH WA/ORE PER WATER VAPOR IMAGERY...WILL ROTATE THROUGH THE BASE OF THE WRN CLOSED LOW ON DAY 1 AND EMERGE FROM THE NRN HIGH PLAINS...TRACKING NNEWD ACROSS THE DAKOTAS ON FRIDAY. IN THE EAST...A SHORTWAVE TROUGH LOCATED OVER THE UPPER OH VALLEY/CENTRAL APPALACHIANS AT THE START OF DAY 2 SHOULD WEAKEN/DE-AMPLIFY AS THIS PROGRESSIVE FEATURE REACHES THE MID-ATLANTIC COAST BY EARLY FRIDAY EVENING. MEANWHILE...WEAK PERTURBATIONS SHOULD MOVE ESEWD FROM THE MIDWEST THROUGH THE OH VALLEY.

...PARTS OF CENTRAL/NRN PLAINS TO UPPER MS VALLEY... SLY LOW LEVEL WINDS EXTENDING INTO THE DAKOTAS WILL SUPPORT NWD MOISTURE RETURN BENEATH THE NRN EXTENSION OF STEEP MIDLEVEL LAPSE RATES EXTENDING ACROSS THE MID MO TO UPPER MS VALLEYS. THIS WILL CONTRIBUTE TO MODERATE TO VERY STRONG INSTABILITY ACROSS THE CENTRAL/NRN PLAINS BY FRIDAY AFTERNOON.

AREAS OF ELEVATED TSTMS WILL LIKELY BE ONGOING FROM THE NRN PLAINS SEWD INTO THE MIDWEST ALONG AND N OF A WARM FRONT AND WITHIN A LOW LEVEL WAA REGIME. PERSISTENT WAA ALONG THE N/NEWD ADVANCING WARM FRONT SHOULD SUPPORT CONTINUED CONVECTION SPREADING N/NEWD ACROSS THE UPPER MS VALLEY.

FORCING FOR ASCENT ATTENDANT TO THE SHORTWAVE TROUGH MOVING ACROSS THE DAKOTAS AND CONVERGENCE ALONG A COLD FRONT ADVANCING EWD THROUGH THE NRN/CENTRAL PLAINS ARE EXPECTED TO SUPPORT NEW TSTM DEVELOPMENT ALONG THE COLD AND WARM FRONTS...POSSIBLY AS FAR S AS ERN KS TO OK. STRONG SHEAR VECTORS ORIENTED PARALLEL TO THE COLD FRONT SUGGESTS ACTIVITY WILL TEND TO BE LINEAR...THOUGH SUPERCELLS WILL BE POSSIBLE. A STRENGTHENING LLJ INTO THE MID-UPPER MS VALLEY SUGGESTS UPSCALE GROWTH INTO ONE OR MORE MCS/S APPEARS LIKELY AS THE COLD FRONT PROGRESSES EWD INTO THE UPPER MS AND LOWER MO VALLEYS. SOME ACTIVITY MAY REMAIN SEVERE GIVEN MODERATE ELEVATED INSTABILITY.

...MID MS VALLEY SEWD THROUGH OH/TN VALLEYS... A WARM FRONT AND RETURNING LOW LEVEL MOISTURE ARE EXPECTED TO SPREAD NEWD INTO THIS REGION BENEATH THE EWD EXTENSION OF STEEP MIDLEVEL LAPSE RATES. SOME MODEL UNCERTAINTY CONTINUES ACROSS IL/IND/OH ON FRIDAY WITH RESPECT TO HOW FAR NE THE WARM FRONT REACHES AND THE OVERALL DEGREE OF DESTABILIZATION DUE TO THE LIKELIHOOD FOR ONGOING CONVECTION/TSTMS FRIDAY MORNING N/NE OF THE FRONT. HOWEVER...GIVEN A NWLY FLOW REGIME ACROSS THIS REGION AND THE 12Z ECMWF/00Z GFS INDICATING A MIDLEVEL IMPULSE MOVING THROUGH THE RIDGE ACROSS THE MIDWEST AND OH VALLEY...CONFIDENCE IS HIGHER FOR GREATER STORM COVERAGE FRIDAY AFTERNOON. MODERATE-VERY STRONG INSTABILITY SHOULD DEVELOP ACROSS IL/IND /MLCAPE OF 2000-3000 J PER KG/ AND MODERATE INSTABILITY ACROSS OH/KY. A 40-50 KT WNWLY MIDLEVEL JET ACCOMPANYING THE IMPULSE INTO WILL RESULT IN EFFECTIVE BULK SHEAR INCREASING TO 35-40 KT SUPPORTIVE OF ORGANIZED STORMS. SHEAR VECTORS ORIENTED MORE PARALLEL TO THE WARM FRONT SUGGEST LINE SEGMENTS SHOULD BE THE PRIMARY MODE...THOUGH SUPERCELLS WILL BE POSSIBLE. GIVEN THESE FACTORS...A SLIGHT RISK AREA HAS BEEN INTRODUCED WITH PRIMARY THREATS BEING DAMAGING WINDS AND HAIL.

...THERE IS A SLGT RISK OF SVR TSTMS EXTENDING FROM THE NRN AND CENTRAL HIGH PLAINS EWD THROUGH THE MID MS/OH VALLEYS TO THE LOWER GREAT LAKES AND PA...

...SYNOPSIS... A BLOCKING PATTERN EXTENDING FROM THE NWRN STATES AND ACROSS CANADA WILL PERSIST INTO DAY 3 /SAT/. THE CLOSED LOW OVER ERN CANADA WILL SHIFT SSEWD ACROSS QUEBEC TOWARD NRN NEW ENGLAND. MEANWHILE...IN THE WEST A CLOSED LOW WILL RETROGRADE NWWD ACROSS SASKATCHEWAN/ ALBERTA AS A TROUGH DIGS SEWD ACROSS THE PACIFIC NW TO THE GREAT BASIN...MAINTAINING THE LONGWAVE TROUGH OVER THE WRN STATES. WITH MORE OF A FLAT RIDGE EXPECTED ACROSS THE SRN HALF OF THE CONUS BY SATURDAY...MID-UPPER LEVEL FLOW FROM THE SWRN STATES TO THE OH VALLEY AND MID-ATLANTIC STATES SHOULD BECOME GENERALLY WSWLY.

AT 12Z SATURDAY...MODELS ARE IN GENERAL AGREEMENT INDICATING A WARM FRONT EXTENDING WNWWD FROM OH TO AN AREA OF LOW PRESSURE LOCATED OVER ERN IA/NRN IL. A COLD FRONT SHOULD BE TRAILING SWWD FROM THE LOW THROUGH ERN KS TO THE SRN HIGH PLAINS. THE SURFACE LOW SHOULD MOVE EWD THROUGH THE OH VALLEY/SRN GREAT LAKES REGION WITH THE COLD FRONT ADVANCING SLOWLY SEWD INTO THE OH AND MID MS VALLEYS. MEANWHILE...THE WARM FRONT WILL MOVE EWD REACHING THE LOWER GREAT LAKES TO MID-ATLANTIC STATES BY 12Z SUNDAY.

...LOWER MO/MID MS VALLEYS TO OH VALLEY/SRN GREAT LAKES... SWLY LOW LEVEL WINDS ACROSS THE WARM SECTOR AND BENEATH A PLUME OF STEEP MIDLEVEL LAPSE RATES SPREADING THROUGHOUT MUCH OF THIS REGION WILL SUPPORT THE DEVELOPMENT OF MODERATE-VERY STRONG INSTABILITY FROM THE UPPER OH VALLEY WSWWD TO KS/OK. THE STRONGEST INSTABILITY SHOULD RESIDE FROM THE MID MS VALLEY INTO ERN KS/NERN OK WITH MLCAPE OF 2500-3500 J/KG. MODELS SUGGEST SEVERAL MIDLEVEL IMPULSES SHOULD TRAVERSE THE OH VALLEY/GREAT LAKES ON SATURDAY AIDING IN NEW TSTM DEVELOPMENT WITHIN THE MOIST/UNSTABLE ENVIRONMENT. EFFECTIVE BULK SHEAR SHOULD BE GREATEST FROM THE UPPER OH VALLEY INTO PA AND LOWER GREAT LAKES WHERE ORGANIZED STORMS WILL BE POSSIBLE. ALTHOUGH BULK SHEAR WILL BE WEAKER WITH WWD EXTENT INTO THE LOWER OH TO LOWER MO VALLEYS...THE DEGREE OF INSTABILITY AND STEEP LAPSE RATES SUGGEST SOME STORMS COULD BECOME SEVERE.

...CENTRAL/NRN HIGH PLAINS EWD ACROSS NEB/KS... DESPITE GENERALLY WEAK LOW LEVEL MOISTURE RETURN INTO THE HIGH PLAINS OF ERN CO TO SERN MT...STEEP MIDLEVEL LAPSE RATES AND STRONG SURFACE HEATING ALONG A DEVELOPING LEE TROUGH WILL RESULT IN MODERATE INSTABILITY /MLCAPE AROUND 1000 J PER KG/. MODELS TEND TO AGREE WITH THE A MIDLEVEL IMPULSE OR TWO SPREADING NEWD ACROSS THE CENTRAL/NRN HIGH PLAINS BY 19/00Z PROVIDING FORCING FOR ASCENT FOR TSTM DEVELOPMENT. EFFECTIVE BULK SHEAR OF 40-50 KT COMBINED WITH THE STEEP LAPSE RATE ENVIRONMENT SUGGESTS SUPERCELLS WILL BE POSSIBLE. MODELS SUGGEST STORMS WILL MOVE OFF THE HIGHER TERRAIN INTO THE WRN DAKOTAS...WITH GREATEST UPSCALE GROWTH INTO AN MCS OR TWO ACROSS THE CENTRAL PLAINS WHERE INSTABILITY WILL BE STRONGER INTO SATURDAY NIGHT TO MAINTAIN SOME SEVERE WEATHER THREAT.

TAKE COVER NOW. MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF ASTURDY BUILDING. AVOID WINDOWS. IF IN A MOBILE HOME...A VEHICLE OROUTDOORS...MOVE TO THE CLOSEST SUBSTANTIAL SHELTER AND PROTECTYOURSELF FROM FLYING DEBRIS.

TO REPORT SEVERE WEATHER...CONTACT YOUR NEAREST LAW ENFORCEMENTAGENCY. THEY WILL RELAY YOUR REPORT TO THE NATIONAL WEATHER SERVICEIN DODGE CITY.

...THERE IS A SLGT RISK OF SVR TSTMS TODAY AND TONIGHT ACROSS THE MID/LOWER MISSOURI AND MIDDLE MISSISSIPPI VALLEYS...

...SYNOPSIS... MODELS INDICATE THAT A VIGOROUS SHORT WAVE IMPULSE WILL BECOME THE PRIMARY LOW CENTER AS IT LIFTS NORTH OF THE NORTHERN ROCKIES THROUGH SOUTHERN SASKATCHEWAN DURING THIS FORECAST PERIOD. BROADER SCALE TROUGHING...WITHIN WHICH THIS FEATURE IS EMBEDDED...LIKELY WILL PERSIST ACROSS MUCH OF THE WESTERN U.S...WHILE CONTINUING TO DEVELOP EASTWARD THROUGH MUCH OF THE NORTHERN PLAINS. AS THIS OCCURS...AND ANOTHER CLOSED LOW DIGS TO THE SOUTHEAST OF JAMES BAY...A REMNANT DOWNSTREAM MID-LEVEL CIRCULATION IS EXPECTED TO MIGRATE ACROSS NORTHERN MID ATLANTIC AND SOUTHERN NEW ENGLAND COASTAL AREAS. MEANWHILE...MID-LEVEL SUBTROPICAL RIDGING MAY BECOME A BIT MORE PROMINENT ACROSS THE SOUTHERN TIER STATES...BUT WEAK HIGH-LEVEL TROUGHING PROBABLY WILL LINGER OVER THE EASTERN GULF OF MEXICO...BETWEEN AN EXPANDING HIGH CENTER OVER THE MEXICAN PLATEAU/RIO GRANDE VALLEY AND ANOTHER OVER THE LOWER LATITUDE ATLANTIC.

...MID/LWR MISSOURI AND MIDDLE MISSISSIPPI VALLEYS... AHEAD OF A WEAK COLD FRONT ADVANCING INTO THE NORTHERN AND CENTRAL PLAINS...AND NORTH/EAST OF A DEEP THERMAL LOW CENTER OVER THE SOUTH CENTRAL PLAINS...A MOIST BOUNDARY LAYER WITH 70F+ SURFACE DEW POINTS IS EXPECTED TO OVERSPREAD THE REGION. THIS APPEARS LIKELY TO OCCUR COINCIDENT WITH THE EASTWARD ADVECTION OF VERY WARM ELEVATED MIXED LAYER AIR...AT LEAST AS FAR EAST AS THE MID AND LOWER MISSOURI VALLEY REGION BY EARLY THIS AFTERNOON. AND A BROAD AREA OF MODERATE TO STRONG INSTABILITY IS EXPECTED TO DEVELOP BY PEAK AFTERNOON HEATING. MIXED LAYER CAPE PROBABLY WILL REACH 2000-4000 J/KG...WITH HIGHEST VALUES CENTERED ACROSS PARTS OF EASTERN KANSAS INTO WESTERN AND CENTRAL MISSOURI.

MID-LEVEL FORCING TO FOCUS STRONGER CONVECTIVE DEVELOPMENT REMAINS UNCLEAR...BUT A BROAD LOW/MID-LEVEL WARM ADVECTION REGIME BENEATH BROADLY DIFLUENT UPPER FLOW SEEMS LIKELY TO PROVIDE SUPPORT FOR CONVECTIVE DEVELOPMENT. AND MOMENTUM/SHEAR ASSOCIATED WITH A BROAD BELT OF 30-40+ KT SOUTHWESTERLY 500 MB FLOW NOSING ACROSS THE CENTRAL PLAINS AND MID MISSOURI VALLEY...AS WELL AS A 30-40 KT SOUTHERLY LOW-LEVEL JET FROM THE SOUTHERN PLAINS INTO THE LOWER MISSOURI VALLEY...PROBABLY WILL CONTRIBUTE TO THE EVOLUTION OF ORGANIZED MESOSCALE CONVECTIVE SYSTEMS CAPABLE OF PRODUCING DAMAGING WIND GUSTS AND HAIL.

THE DETAILS OF THE CONVECTIVE EVOLUTION REMAIN FAR FROM CERTAIN. HOWEVER...IT APPEARS POSSIBLE THAT A REMNANT IMPULSE OR MESOSCALE CONVECTIVE VORTEX...ASSOCIATED WITH THE LARGE ONGOING CONVECTIVE CLUSTER ACROSS THE MID MISSOURI VALLEY...COULD PROVIDE THE FOCUS FOR NEW DEVELOPMENT THIS AFTERNOON FROM PARTS OF EASTERN NEBRASKA/WESTERN IOWA INTO NORTHERN MISSOURI. ADDITIONAL DEVELOPMENT MAY THEN OCCUR LATE THIS AFTERNOON AND EVENING ON ITS WESTERN FLANK...ACROSS EASTERN KANSAS INTO WESTERN MISSOURI...AS ANOTHER IMPULSE EMERGING FROM THE INTERMOUNTAIN WEST WEAKENS STRONG INHIBITION ACROSS THE CENTRAL PLAINS.

...THERE IS A SLGT RISK OF SVR TSTMS FROM PORTIONS OF OK/KS EWD INTO THE OH VALLEY...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE NRN AND CENTRAL HIGH PLAINS...

...SYNOPSIS... A BLOCKING UPPER RIDGE FROM THE GREAT LAKES REGION NWWD INTO THE CENTRAL CANADIAN PROVINCES WILL MAINTAIN A BROAD TROUGH OVER MOST OF THE WRN/CENTRAL CONUS AND ANOTHER TOUGH ACROSS THE NERN STATES. THE WRN/CENTRAL U.S TROUGH WILL FLATTEN THE RIDGE ACROSS THE SOUTH STATES AND RESULT IN RELATIVELY STRONG WSWLY MID LEVEL WINDS FROM THE CENTRAL ROCKIES/PLAINS EWD THROUGH THE OH VALLEY AND INTO NEW ENGLAND. IN ASSOCIATION WITH THE TWO UPPER TROUGHS ...A WEAK COLD FRONT IS FORECAST TO STRETCH FROM NEW ENGLAND SWWD THROUGH THE OH/MID MS VALLEYS AND INTO CENTRAL OK/SRN TX PANHANDLE LATE SATURDAY AFTERNOON.

...OH VALLEY REGION... OPERATIONAL MODELS ARE SUGGESTIVE THAT AN MCS MAY BE LOCATED OVER PORTIONS OF MO/IL AT THE START OF THE PERIOD...WITHIN ZONE OF LOW LEVEL WARM ADVECTION. THIS ACTIVITY IS LIKELY TO SPREAD EWD THROUGH THE OH VALLEY DURING THE DAY AND EITHER REINTENSIFY OR NEW STORMS DEVELOP ALONG THE FRONT AND OUTFLOW BOUNDARIES. IN AREAS WHERE STRONG HEATING OCCURS...THE COMBINATION OF DEWPOINTS IN THE UPPER 60S/LOWER 70S AND STEEP MID LEVEL LAPSE RATES WILL RESULT IN A VERY UNSTABLE AIR MASS. GIVEN THAT THE EFFECTIVE BULK SHEAR WILL BE IN THE 25-35 KT RANGE WITH MOSTLY UNIDIRECTIONAL WLY WINDS...A LINEAR MCS OR TWO IS POSSIBLE WITH WIND DAMAGE THE PRIMARY SEVERE THREAT.

...OK/KS/MO AREA... STORMS/CLOUDS ARE EXPECTED TO SHIFT EWD OUT OF MO IN THE MORNING ...WHICH SHOULD RESULT IN STRONG HEATING OF MOIST BOUNDARY LAYER...ESPECIALLY NEAR THE FRONT IN KS/OK. MODELS INDICATE THAT THE COMBINATION OF TEMPERATURE NEAR 100 AND DEWPOINTS IN THE MID 60S WILL RESULT IN EXTREME INSTABILITY. HOWEVER...VERY WARM MID LEVEL TEMPERATURES...14 TO 16C AT 700 MB... ARE EXPECTED TO INHIBIT CONVECTION THROUGH MUCH OF THE DAY. HOWEVER...00Z NAM/GFS BOTH SHOW THE SRN END OF A SHORTWAVE TROUGH MOVING THROUGH WRN KS/TX PANHANDLE LATE IN THE DAY. FORCING AHEAD OF THIS FEATURE AND FRONTAL CONVERGENCE MAY BE ENOUGH FOR HIGH BASED STORMS TO DEVELOP LATE IN THE DAY...ESPECIALLY AS TEMPERATURES CLIMB ABOVE 100 DEGREES. MID LEVEL WLY WINDS AT 35-45 KT WILL HELP ORGANIZE/SUSTAIN STORMS AND A VERY FAVORABLE THERMODYNAMIC ENVIRONMENT WILL EXIST FOR HAIL AND SEVERE WIND GUSTS...SOME WIND GUSTS WHICH MAY BE SIGNIFICANT. STORMS MAY SPREAD OR REDEVELOP DURING THE EVENING INTO SRN MO AS THE UPPER TROUGH SHIFTS EWD AND THE LOW LEVEL JET STRENGTHENS...WITH A CONTINUED THREAT FOR WIND DAMAGE AND HAIL.

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE NRN/CENTRAL PLAINS EWD THROUGH INTO THE MID MS AND OH VALLEYS...

...SYNOPSIS... IMPRESSIVE SHORTWAVE TROUGH AND ASSOCIATED JET MAX ARE FORECAST TO MOVE DOWN THE BACKSIDE OF THE WRN U.S UPPER TROUGH...RESULTING IN THE LARGER SCALE TROUGH TO AMPLIFY WEST OF THE ROCKIES. CONSEQUENTLY...IN AGREEMENT WITH GFS/EURO SOLUTIONS...SHORTWAVE RIDGING AND STRONGER MID LEVEL WLY FLOW WILL BE PUSHED NWD ACROSS THE PLAINS STATES...AND EXTEND FROM NM NEWD INTO KS/NEB AND THEN EWD THROUGH THE LOWER OH VALLEY AND INTO THE MID ATLANTIC STATES. IN RESPONSE TO THE AMPLIFYING UPPER TROUGH...SURFACE LOW PRESSURE SHOULD DEVELOP IN ERN CO...WITH A WARM/STATIONARY FRONT EXTENDING EWD ACROSS KS THROUGH SRN MO AND INTO THE OH VALLEY.

...MID MS AND OH VALLEY REGION... SWLY LOW LEVEL JET IS FORECAST TO IMPINGE UPON FRONT ACROSS SRN MO...WITH CONVECTION LIKELY TO BE ONGOING OVER PORTIONS OF ERN MO EWD INTO INDIANA SUNDAY MORNING. WHILE THE SHEAR AND INSTABILITY WOULD SUPPORT A MARGINAL SEVERE THREAT...THE STORMS SHOULD INTENSIFY DURING THE AFTERNOON AS WARMING TEMPERATURES RESULT IN STRONGLY UNSTABLE AIR MASS. THE DEEP WLY TROPOSPHERIC WINDS AND 30-40 KT MID LEVEL FLOW SHOULD FAVOR AN ORGANIZED LINE OR TWO WITH WIND DAMAGE THE MOST LIKELY THREAT.

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRALILLINOIS...EAST CENTRAL ILLINOIS AND SOUTHEAST ILLINOIS.

.DAY ONE...TODAY AND TONIGHT

A WARM MOIST AIRMASS WILL INTERACT WITH A WARM FRONT TO THE WEST TOBRING THUNDERSTORMS TO THE AREA FOR LATE THIS AFTERNOON AND TONIGHT.THERE IS A SLIGHT RISK THAT SOME OF THESE STORMS COULD BECOMESEVERE WITH DAMAGING WINDS AND LARGE HAIL.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED LATER THIS AFTERNOON AND INTOTONIGHT.

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EAST CENTRALWISCONSIN...SOUTH CENTRAL WISCONSIN AND SOUTHEAST WISCONSIN.

.DAY ONE...TODAY AND TONIGHT

PATCHY DENSE FOG IS EXPECTED TO LINGER ACROSS EASTERNSHEBOYGAN...OZAUKEE AND MILWAUKEE COUNTIES UNTIL MID MORNING.

THERE IS A CHANCE OF THUNDERSTORMS THIS AFTERNOON SOUTHWEST OFMADISON...AS AN UPPER LEVEL DISTURBANCE CROSSES THE REGION.THUNDERSTORMS BECOME LIKELY TONIGHT FROM WEST TO EAST ACROSS THEAREA...AS A WARM FRONT MOVES NORTH TOWARD THE AREA...AND ANOTHERUPPER LEVEL DISTURBANCE CROSSES THE REGION.

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TONIGHT...MAINLYSOUTHWEST OF A MINERAL POINT TO MONROE LINE. LARGE HAIL...DAMAGINGWINDS AND HEAVY RAINFALL WOULD BE POSSIBLE IN THIS AREA...AS APOSSIBLE COMPLEX OF THUNDERSTORMS MOVES ACROSS THE REGION.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

CHANCES FOR THUNDERSTORMS WILL CONTINUE AT TIMES SATURDAY THROUGHTHURSDAY...AS THE WARM FRONT SLOWLY MOVES NORTH TOWARD AND THROUGHTHE AREA. SEVERAL UPPER LEVEL DISTURBANCES ARE EXPECTED TO SHIFTACROSS THE REGION DURING THIS TIME.

THE BEST CHANCES FOR THUNDERSTORMS WOULD BE SATURDAY...AS APOSSIBLE THUNDERSTORM COMPLEX MOVES THROUGH THE REGION...ANDTUESDAY NIGHT...AS A COLD FRONT MOVES THROUGH. IF THE COMPLEXMOVES THROUGH ON SATURDAY...HEAVY RAINFALL WOULD BE POSSIBLE.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TONIGHT SOUTHWEST OF MADISON...ANDAT TIMES LATER THIS WEEKEND INTO NEXT WEEK ACROSS THE AREA.

.DISCUSSION...ISSUED 1123 AM CDT FRI JUN 17 2011MINOR TWEAKS TO THE FORECAST TO COVER FOR THE PRECIP SHIELD ANDWEATHER ADVANCING FROM THE WEST. STILL CONCERN FOR AFTERNOONTHUNDERSTORMS...WITH IMPRESSIVE LAPSE RATES ON 12Z SOUNDING. THATBEING SAID...SHEAR IS MINIMAL AND SFC BASED INSTABILITY IS GETTINGLIMITED BY CLOUD COVER/PRECIP SHIELD FROM APPROACHING CONVECTION.OUTFLOW FROM STORMS WILL HAVE TO BE WATCHED CLOSELY FOR ANYAFTERNOON CONVECTION AHEAD OF THE WARM FRONT THIS EVENING.

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NRN AND CNTRL HIGH PLAINS...KS/OK...AND THE MID MS VALLEY INTO THE OH/TN VALLEYS...

CORRECTED FOR GRAPHIC

...SYNOPSIS... AN UPPER RIDGE OVER THE MO/MS VALLEY REGION WILL FLATTEN THROUGH THE DAY AND SHIFT EWD A BIT AS MULTIPLE EMBEDDED SHORTWAVES ALOFT MOVE INTO THE PLAINS. ONE SUCH SHORTWAVE TROUGH WILL MOVE FROM NM NEWD ACROSS THE TX/OK PANHANDLES DURING THE DAY AND ACROSS KS/OK AND INTO WRN MO BY SUN MORNING. ANOTHER WAVE WILL MOVE ACROSS WY/CO AND INTO NEB DURING THE AFTERNOON AND EVENING.

AT THE SURFACE...A WEAK COLD FRONT WILL EXTEND FROM ERN KS INTO THE TX PANHANDLE...WITH A DRYLINE EXTENDING SWWD FROM A WRN OK LOW INTO TX. AS THE UPPER WAVES APPROACH...THE COOL AIR BEHIND THE OLD FRONT WILL MIX AND WINDS WILL VEER TO ELY OVER KS...ALLOWING MOISTURE TO BACK WWD AND RESULTING IN A WARM FRONT NEAR THE KS/OK BORDER. MEANWHILE...A SHARP DRYLINE WILL EXIST ALONG THE I-35 CORRIDOR FROM THE KS/OK BORDER SWD INTO NRN TX. BOTH THESE FEATURES WILL BE THE FOCUS FOR SEVERE STORMS.

TO THE N...WEAK LEE TROUGHING WILL EXTEND NWD INTO WY...WRN SD AND NEB BY AFTERNOON...HELPING TO FOCUS CONVECTION IN THIS AREA AS WELL.

TO THE E...MODERATE NWLY FLOW ALOFT WILL EXIST ON THE E SIDE OF THE RIDGE AXIS ACROSS THE OH AND TN VALLEYS...WITH SIGNS OF WEAK EMBEDDED FEATURES POSSIBLY ASSOCIATED WITH ONGOING CONVECTION.

...OH/TN VALLEY REGION... CONSIDERABLE UNCERTAINTY EXISTS IN REGARD TO PLACEMENT AND EVOLUTION OF MORNING CONVECTION...BUT CONSENSUS IS THAT A POSSIBLE MCS WILL BE ONGOING OVER IND...KY...AND SWRN OH SAT MORNING...TIED TO A POSSIBLE SHORTWAVE TROUGH ROUNDING THE RIDGE AND FORCED ON THE NOSE OF A SWLY LOW LEVEL JET. THESE STORMS WILL HAVE MAINLY A WIND THREAT...AND MAY REGENERATE/STRENGTHEN DURING THE DAY WITH AREAS OF HEATING TO THE S. THERE MAY ALSO BE A MARGINAL HAIL THREAT ESPECIALLY ON THE SRN AND WRN FLANK OF ANY STORM CLUSTER...IN CLOSE PROXIMITY TO BETTER LOW LEVEL LAPSE RATES AND THUS STRONGER UPDRAFTS.